Composite rotor blade retention

ABSTRACT

A system for transferring the dynamic loading forces from a composite rotor blade held between external and internal metallic fittings. A lock nut in communication with a key serves to transmit torque from the internal fitting to the root end socket by preloading against the composite structure to induce compressive hoop stresses therein.

United States Patent inventor Tadeusz Tarcrynslti Ridley Park, Pa.853,873 Aug. 28, 1969 Sept. 7, 1971 The United States oi America asrepresented by the Secretary of the Air Force Appl. No. Filed PatentedAssignee COMPOSITE ROTOR BLADE RETENTION 3 Claims, 2 Drawing Figs.

u.s.c|. 416/204, 416/230 lnt.Cl. 1364c 27/48 Field oiSearch.. 416/229,

[56] References Cited UNITED STATES PATENTS 2,297,142 9/1942 German4l6/239 (X) 2,303,707 12/ l 942 Pullin 416/209 3,237,697 3/1966 Ford etal. 416/229 (X) 3,303,889 2/1967 Bates 416/241 (X) Primary Examiner-Everette A. Powell, Jr.

Anomeys- Harry A. Herbert, Jr. and Arsen Tashjian PATENTEDSEP nan3.603.701

INVENTOR. mil/.512 774x02: wax! COMPOSITE ROTOR BLADE RETENTIONBACKGROUND OF THE INVENTION This invention relates to a root fittingarrangement for mechanically retaining a composite rotor blade to arotor hub and, more particularly, the invention is concerned withproviding a root fitting which effectively transfers dynamic loadingfrom a composite blade structure exhibiting poor mechanical attachmentproperties to metal fittings which exhibit good mechanical attachmentproperties.

In rotor blades of advanced composite structure, the problem arises oftransmitting the dynamic loads to the rotor hub. The torque, tension,and bending loads of the rotor blade must be transmitted to the rotorhub through the metal root end fitting. Thus, the attachment meansshould provide a path for loads from the composite structure to therotor hub.

SUMMARY OF THE INVENTION The present invention provides a compositerotor blade retention means whereby the torque, tension and bendingloads are transmitted from the rotor blade to the rotor hub. In theregion of attachment, a blade internal fitting is provided with areverse taper which by wedging action creates hoop tension stresses inthe blade molded composite structure, whose bursting under thesestresses is prevented by the restraining action of the root end socketpreloaded against the composite structure by means of a nut. Thisconfiguration locks the blade against pull out.

An internal fitting is provided with a fluted portion for transmittingtorque from the blade structure to the internal fitting. A key transmitsthe torque from the internal fitting to the root end socket and a nutpreloads the root end socket against the molded composite structure forinducing compressive hoop stresses therein. This arrangement provides anadditional path for torque from the composite structure to the outerfitting by friction.

Accordingly, it is an object of the invention to provide a compositerotor blade retention having an internal fitting and root end socketwherein torque, tension and bending loads are transmitted to the rotorhub.

Another object of the invention is to provide a composite rotor bladeretension wherein a key transmits the torque from the internal fittingto the root end socket.

Still another object of the invention is to provide a composite bladeretention wherein a nut operates to preload the root end socket againstthe molded composite structure to induce compressive hoop stressestherein.

A further object of the invention is to provide fluting in the internalfitting to transmit torque from the blade structure to the internalfitting.

These and other objects, features, and advantages will become moreapparent after considering the description that follows taken inconjunction with the attached drawings wherein like numbers are usedthroughout to refer to like elements.

IN THE DRAWING FIG. I is a plan view of a rotor blade showing the bladeattach lug; and

FIG. 2 is an enlarged view in cross section of the blade attach lugtaken along the line 22 showing the details of the blade retentionaccording to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings,there is shown a rotor blade generally identified by the referencenumeral l3 having a blade attach lug 15 attached to the root end of theblade. The details of the lug 15 are shown in enlarged detail in FIG. 2and include the root end fitting 17 of tapered configuration extendingfrom the rotor blade attach centerline 219 outwardly.

An internal fitting 21 is positioned inside in spaced relation to theouter fitting 17. The molded composite structure retained between theinner fitting 211 and the outer fitting ll? is reverse tapered, that is,the thickness dimension starts large and uniformly decreases as itapproaches the outer ends of the fittings. This configuration provideslock against pull out of the rotor blade 13 from the fittings. Thefluting 23 is included in the internal fitting 21 for transmittingtorque from the blade structure 13 to the internal fitting Zll.

A key 25 is positioned at the root end socket between the inner ends ofthe internal and outer fittings and serves to transmit torque from theinternal fitting 21 to the root end socket. A nut 27 serves to preloadthe root end socket against the molded composite structure of the rotorblade 13. In this way compressive hoop stresses are induced in themolded com posite structure and provide an additional path for torquefrom the composite structure to the outer fitting 17 by friction.

It will be appreciated that the design of the attachment of the advancedcomposite rotor blade to a metal root end fitting enables the use ofcomposites in rotorcraft having a pin connection of the blades to thetransmission system. The use of advanced composite design results inmuch improved blades having the potential of substantial operationalimprovements for all classes of rotorcraft.

W Although the invention has been illustrated in the accompanyingdrawings and described in the foregoing specification in terms of apreferred embodiment thereof, the invention is not limited to thisembodiment or to the particular configuration mentioned. It will beapparent to those skilled in the art that my invention could haveextensive use as composite blades become operational and will produceoperational improvement in all classes of rotorcraft.

Also, it should be understood that various changes, alterations,modifications and substitutions, particularly with respect to theconstruction details, can be made in the arrangement of the severalelements without departing from the true spirit and scope of theappended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. A rotor blade retention means including a root end socket comprisinga molded rotor blade structure, a tapered outer fitting extendingoutwardly from the blade attach centerline over said rotor bladestructure, a correspondingly tapered internal fitting positioned inspaced relation to said outer fitting inside said rotor blade structure,a key positioned between the inner end of said internal fitting and saidouter fitting, said key transmitting torque from said internal fittingto the root end socket, and a nut adjacent the inner surface of saidkey, the adjustment of said nut preloading the root end socket againstthe inner portion of the composite rotor blade thereby inducingcompressive hoop stresses therein.

2. The rotor blade retention means defined in claim wherein the moldedcomposite structure retained between said outer and internal fittings isreverse tapered, the configuration of the socket being larger at theinner end and uniformly decreasing dimensionally toward the outer end.

3. The rotor blade retension means defined in claim 2 wherein theinternal fitting is fluted near the outer portion, the fluting operatingto transmit torque from the rotor blade structure to the internalfitting.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,603,701 Dated September 7, 1971 Inventor(s) TADEUSZ TARCZYNSKI It iscertified that error appears in the aboveidentified patent and that saidLetters Patent are hereby corrected as shown below:

The name of the inventor where it appears on the cover page of theissued patent is misspelled; the correct spelling is TADEUSZ TARCZYNSKI.

Signed and sealed this 8th day of February 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting ffi Commissioner ofPatents )RM PO-105O (10-69]

1. A rotor blade retention means including a root end socket comprisinga molded rotor blade structure, a tapered outer fitting extendingoutwardly from the blade attach centerline over said rotor bladestructure, a correspondingly tapered internal fitting positioned inspaced relation to said outer fitting inside said rotor blade structure,a key positioned between the inner end of said internal fitting and saidouter fitting, said key transmitting torque from said internal fittingto the root end socket, and a nut adjacent the inner surface of saidkey, the adjustment of said nut preloading the root end socket againstthe inner portion of the composite rotor blade thereby inducingcompressive hoop stresses therein.
 2. The rotor blade retention meansdefined in claim 1 wherein the molded composite structure retainedbetween said outer and internal fittings is reverse tapered, theconfiguration of the socket being larger at the inner end and uniformlydecreasing dimensionally toward the outer end.
 3. The rotor bladeretension means defined in claim 2 wherein the internal fitting isfluted near the outer portion, the fluting operating to transmit torquefrom the rotor blade structure to the internal fitting.